A tracheal tube is a medical device commonly used in intensive care and during operations under general anesthesia. It consists of a flexible tube with the distal end surrounded by a cuff. When inserted into the trachea, inflation of this cuff seals the tube to the tracheal wall. This facilitates ventilation and also secures the patient's airway from aspiration of gastric contents and other foreign material.
Conventionally, air or other fluid is injected into the tracheal cuff by means of an inflation syringe attached to a pilot balloon. This system has many inherent disadvantages. Manual inflation by syringe is inconvenient, sometimes requires the assistance of a second party and delays the inflation of the cuff. It is especially important to protect the patient's airway when the risk of aspiration of gastric contents is high, as in anaesthesia for caesarean section, traumatized patients and operations for acute abdominal conditions. It is in these situations that a system is especially indicated which provides rapid and non-manual inflation of the tracheal cuff, eliminating time delay and need for assistance during intubation of the trachea.
Over compression of the tracheal mucosa by the inflated cuff is another problem with the conventional tracheal tube inflator. The pressure of the tracheal cuff can only be estimated crudely by palpation of the pilot balloon. With manual inflation, the tracheal cuff pressure may frequently exceed the desired pressure of approximately 20 mm Hg. In addition, during general anaesthesia with nitrous oxide, diffusion of nitrous oxide into the tracheal cuff will increase the pressure exerted on the tracheal wall. This results in a high incidence of complications such as sore throat, hoarseness and tracheal damage after removal of the tube. To prevent this, the cuff pressure must be checked and adjusted frequently. This is inconvenient and time consuming and seldom done in practice.
These problems are addressed in the applicant's U.S. patent 4,649,914 which describes an inflator for a tracheal cuff that includes an inner flexible balloon surrounded by an outer balloon of higher compliance. At the upstream end of the inner balloon is an inflation/deflation valve. A control valve is connected to the downstream end of both balloons and to an inflating tube for the tracheal cuff to pass pressurized air from the inner balloon to the inflating tube and to connect the inflating tube to the outer control balloon.
In use, the inner balloon is inflated or "preloaded" through the upstream valve. At the appropriate moment, the downstream valve is opened to cause rapid inflation of the cuff. The outer balloon then acts in concert with the cuff to maintain substantially constant pressure in the cuff.
The present invention is concerned with the provision of improved inflator configurations for this purpose.